Progressive collapse has been an important issue in building failures since the
collapse of the Ronan Point apartment building in 1968. Progressive collapse is a failure
sequence that relates local damage to large scale collapse in a structure. If any load exceeds
the load-carrying capacity of any member, it will cause additional local failures. Such
sequential failures can propagate through the structure. Therefore, a local member failure
analysis is the basic element for the progressive collapse analysis.
Three different failure criteria have been considered in this study. They are material
failure, buckling failure, and connection failure. Material and buckling failures were
analyzed by using a second-order inelastic method. Connection failures were analyzed by
using a moment-curvature relationship calculated by a power model using three parameters.
The finite element code ABAQUS/Explicit has been used for the analyses. Single
column failure results from the ABAQUS/Explicit simulations and from the NFA
developed for this study based on the second-order inelastic method were compared for a
verification purpose.
Various numbers of spans and stories with rigid, semi-rigid, and reinforced semirigid
frames were studied for 2D frame analyses. As the number of spans increased, the
collapse mode tended to change from total collapse to partial collapse. As the number of
stories increased, the collapse mode tended to change from partial collapse to total collapse.
However, the analyses of the semi-rigid frames showed different trends. All semi-rigid
iii
frames collapsed partially by joint failures. The 2D frame analyses showed that a vertical
failure was caused by connection failures, a horizontal failure was caused by column
buckling.
The 3D frame analyses showed a different tendency. Four different span frames
with rigid and semi-rigid connection with a single column size, were used for six initial
failure cases. The assumed rigid and semi-rigid connection did not make a big difference
in the 3D cases. Therefore, semi-rigid connection would not be a critical factor if the initial
damage is localized. Inner columns were more critical than outer columns.
However, the single column initial failure caused total collapse for the most of the
frame with a more realistic design. The 3D frame with realistic designs showed three facts.
First, a more realistic design, using two different column sizes, is more vulnerable to
progressive collapse than a single size column design. Second, a semi-rigid connection
could trigger total collapse of a structure, while a rigid frame just caused internal damage.
Third, the lengths of columns did not affect collapse modes. However, it could be a factor
when the frame is overdesigned to resist progressive collapse.
iv